1. Field of the Invention
The invention relates to an eccentric screw pump with a pump casing having an intake stub and a delivery stub and enclosing a suction and a delivery chamber. The pump has delivery elements adapted to be driven by a motor in the form of a casing insert and an eccentric screw arranged in the pump casing.
2. Description of the Related Art
The method of delivery of conventional eccentric screw pumps makes them suitable to convey a gas with the liquid. However, in the case of high gas rates in the liquid or dry running of gas, the friction heat engendered between the delivery elements can no longer be dissipated. The term dry running of gas is intended to mean the condition when no liquid is in the gas, and will be referred to hereinafter as to the state when only gas is being delivered by the pump. This undissipated heat results in the stator formed of elastomer being thermally destroyed after a few seconds of operation.
In the case of overloading by excess pressure caused, for example, by a blockage of the delivery line, conventional eccentric screw pumps continue to build up pressure until the elastomer of the delivery unit lifts off from the sealing line and the pumping medium flows back within the delivery unit. During this process, the power consumption of the pump rises proportionally to the differential pressure between the delivery chamber and the suction chamber.
In the case of an overdimensioned driving motor, when an excess pressure occurs the pump continues to turn but the frictional heat engendered can no longer be dissipated by the stationary pumping medium. This also results in the elastomeric stator being thermally destroyed within a short time. Alternatively, if the driving motor is adequately dimensioned for the operating conditions, the pump is brought to a halt in the event of overloading by excess pressure. This can lead to destruction of the electric motor used to drive the pump.